I am trying to learn sympy by plotting Lissajous curves. I am familiar with
python and know some math. I downloaded and installed the Anaconda package
for Windows. I have been able to get a simple curve plotted but the
attached text file shows the few statements and a plot command which gives
a "TypeError: can't convert expression to float" I have tried defining the
symbols as real=true but that did not help. Is the plotting converting a
float to a complex then complaining that it cannot convert a complex to
float? What is the problem with my code?
Attached is a short text file with statements and error. Thanks for your
help.
https://en.wikipedia.org/wiki/Lissajous_curve
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Jupyter QtConsole 4.1.1
Python 3.5.1 |Anaconda 2.5.0 (64-bit)| (default, Jan 29 2016, 15:01:46) [MSC
v.1900 64 bit (AMD64)]
Type "copyright", "credits" or "license" for more information.
IPython 4.0.3 -- An enhanced Interactive Python.
? -> Introduction and overview of IPython's features.
%quickref -> Quick reference.
help -> Python's own help system.
object? -> Details about 'object', use 'object??' for extra details.
%guiref -> A brief reference about the graphical user interface.
from sympy import *
init_session()
IPython console for SymPy 0.7.6.1 (Python 3.5.1-64-bit) (ground types: python)
These commands were executed:
from __future__ import division
from sympy import *
x, y, z, t = symbols('x y z t')
k, m, n = symbols('k m n', integer=True)
f, g, h = symbols('f g h', cls=Function)
init_printing()
Documentation can be found at http://www.sympy.org
from sympy.plotting import (plot, plot_parametric,
plot3d_parametric_surface, plot3d_parametric_line,
plot3d)
from sympy.polys.polyfuncs import interpolate
ampx, ampy, freqx, freqy, theta = symbols('ampx ampy freqx freqy theta',
real=true)
frictionx, frictiony = symbols('frictionx, frictiony', real=true)
tmin, tmax = symbols('tmin, tmax', real=true)
frictionx = interpolate([(tmin, 0.0), (tmax, ln(0.5))], t)
frictiony = interpolate([(tmin, 0.0), (tmax, ln(0.5))], t)
x = ampx * frictionx * sin(freqx * t + theta)
y = ampy * frictiony * sin(freqy * t)
varx = {'ampx':1.0, 'freqx':3.0, 'theta':pi/4.0, 'frictionx': frictionx}
vary = {'ampy':2.0, 'freqy':1.0, 'frictionx': frictionx}
tmin = 0.0
tmax = 4.0 * pi
plot_parametric(x.subs(varx), y.subs(vary), (t, tmin, tmax))
---------------------------------------------------------------------------
TypeError Traceback (most recent call last)
K:\Documents\z_Programs\Anaconda\lib\site-packages\sympy\plotting\experimental_lambdify.py
in __call__(self, args)
193 #The result can be sympy.Float. Hence wrap it with complex
type.
--> 194 result = complex(self.lambda_func(args))
195 if abs(result.imag) > 1e-7 * abs(result):
<string> in <lambda>(x0)
K:\Documents\z_Programs\Anaconda\lib\site-packages\sympy\core\expr.py in
__complex__(self)
229 re, im = result.as_real_imag()
--> 230 return complex(float(re), float(im))
231
K:\Documents\z_Programs\Anaconda\lib\site-packages\sympy\core\expr.py in
__float__(self)
224 raise TypeError("can't convert complex to float")
--> 225 raise TypeError("can't convert expression to float")
226
TypeError: can't convert expression to float
During handling of the above exception, another exception occurred:
TypeError Traceback (most recent call last)
<ipython-input-8-8f9ff98dad6e> in <module>()
----> 1 plot_parametric(x.subs(varx), y.subs(vary), (t, tmin, tmax))
K:\Documents\z_Programs\Anaconda\lib\site-packages\sympy\plotting\plot.py in
plot_parametric(*args, **kwargs)
1409 plots = Plot(*series, **kwargs)
1410 if show:
-> 1411 plots.show()
1412 return plots
1413
K:\Documents\z_Programs\Anaconda\lib\site-packages\sympy\plotting\plot.py in
show(self)
183 self._backend.close()
184 self._backend = self.backend(self)
--> 185 self._backend.show()
186
187 def save(self, path):
K:\Documents\z_Programs\Anaconda\lib\site-packages\sympy\plotting\plot.py in
show(self)
1016
1017 def show(self):
-> 1018 self.process_series()
1019 #TODO after fixing
https://github.com/ipython/ipython/issues/1255
1020 # you can uncomment the next line and remove the pyplot.show()
call
K:\Documents\z_Programs\Anaconda\lib\site-packages\sympy\plotting\plot.py in
process_series(self)
895 # Create the collections
896 if s.is_2Dline:
--> 897 collection = self.LineCollection(s.get_segments())
898 self.ax.add_collection(collection)
899 elif s.is_contour:
K:\Documents\z_Programs\Anaconda\lib\site-packages\sympy\plotting\plot.py in
get_segments(self)
627 list_segments.append([p, q])
628
--> 629 f_start_x = f_x(self.start)
630 f_start_y = f_y(self.start)
631 start = [f_start_x, f_start_y]
K:\Documents\z_Programs\Anaconda\lib\site-packages\sympy\plotting\experimental_lambdify.py
in __call__(self, args)
226 use_evalf=True,
227
complex_wrap_evalf=True)
--> 228 result = self.lambda_func(args)
229 warnings.warn('The evaluation of the expression is'
230 ' problematic. We are trying a failback method'
<string> in <lambda>(x0)
K:\Documents\z_Programs\Anaconda\lib\site-packages\sympy\core\expr.py in
__complex__(self)
228 result = self.evalf()
229 re, im = result.as_real_imag()
--> 230 return complex(float(re), float(im))
231
232 def __ge__(self, other):
K:\Documents\z_Programs\Anaconda\lib\site-packages\sympy\core\expr.py in
__float__(self)
223 if result.is_number and result.as_real_imag()[1]:
224 raise TypeError("can't convert complex to float")
--> 225 raise TypeError("can't convert expression to float")
226
227 def __complex__(self):
TypeError: can't convert expression to float
